U.S. Pat. No. 4,168,396 to Best discloses a microprocessor for executing enciphered programs. Computer programs which have been enciphered during manufacture to deter the execution of the programs in unauthorized computers, must be decrypted before execution. The disclosed microprocessor deciphers and executes an enciphered program one instruction at a time, instead of on a continuous basis, through a combination of substitutions, transpositions, and exclusive OR additions, in which the address of each instruction is combined with the instruction. Each unit may use a unique set of substitutions so that a program which can be executed on one microprocessor cannot be run on any other microprocessor. Further, Best cannot accommodate a mixture of encrypted and plain text programs.
U.S. Pat. No. 4,120,030 to Johnstone describes a computer in which the data portion of instructions are scrambled and in which the data is of necessity stored in a separate memory. There is no disclosure of operating with instructions which are completely encrypted with both the operation code and the data address portion being unreadable without a corresponding key kernel.
U.S. Pat. No. 4,183,085 describes a technique for protecting software by providing two separate program storages. The first program storage is a secure storage and the second program storage is a free storage. Security logic is provided to check whether an output instruction has originated in the secure store and to prevent operation of an output unit which receives output instructions from the free storage. This makes it difficult to produce information by loading a program into free storage.
U.S. Pat. No. 3,996,449 entitled "Operating System Authenticator," discloses a technique for authenticating the validity of a plain text program read into a computer, by exclusive OR'ing the plain text of the program with a key to generate a code word which must be a standard recognizable code word which is successfully compared with a standard corresponding code word stored in the computer. If there is a successful compare, then the plain text program is considered to be authenticated and is allowed to run, otherwise the program is not allowed to run.